Image display

ABSTRACT

This invention is an image display device for performing color display of an image using two spatial light modulators. The image display device has a first spatial light modulator ( 52 ) for modulating a first wavelength range component of illuminating light from an illuminating light source ( 10 ), dichroic mirrors ( 40 ), ( 41 ) for separating second and third wavelength range components of the illuminating light and condensing the respective wavelength range components, a second spatial light modulator ( 50 ) for modulating the second and third wavelength range components, and a dichroic mirror ( 60 ) for combining modulated light emitted from the first and second spatial light modulators ( 52 ), ( 50 ).

BACKGROUND OF THE INVENTION

This invention relates to an image display device, and particularly to aprojection-type image display device and a virtual image display device.

BACKGROUND ART

Conventionally, with respect to an image display device such as aprojection-type image display device or a virtual image display deviceusing a spatial light modulator, the following proposals have been inorder to realize color image display.

(1) One spatial light modulator is used and pixels for R (red), G(green) and B (blue), respectively, are spatially arranged in thespatial light modulator. Color image display is realized by using atleast these three basic color pixels as a set and making each colorpixel smaller than a size that can be recognized with the spatialresolution of human eyes.

Systems for this include a system in which a color filter is providedfor each pixel, a color filterless system using a dichroic mirror and amicrolens array, for example, as described in JP-A-4-60538, and a colorfilterless system using a holographic optical element, for example, asdescribed in JP-A@-189809.

(2) In a “field sequential color system” where one spatial lightmodulator is used and three colors R (red), G (green) and B (blue) ofilluminating light illuminating the element is time-divisionallyswitched, color image display is realized by at least shortening theswitching time to less than a time that can be recognized with thetemporal resolution of human eyes. A fundamental difference between thissystem and the first system is that the spatial light modulatorconstantly modulates only one of R (red), G (green) and B (blue) atarbitrary timing over the entire display area. As the element fortime-divisionally switching the color components, for example, “TimeSequential System” manufactured by Color Link may be used.

(3) Color image display is realized by using three spatial lightmodulators for R (red), G (green) and B (blue), respectively, andcausing color combination means to combine images of the respectivecolors emitted from these spatial light modulators, for example, asdescribed in JP-A-6-202004.

(4) Color image display is realized by combining the second system withthe third system, that is, by using a first spatial light modulator thatconstantly modulates only one of R (red), G (green) and B (blue) atarbitrary timing and a second spatial light modulator that modulates theremaining two colors in the “field sequential color system”. Modulatedlight from the first spatial light modulator and modulated light fromthe second spatial light modulator are combined by color combinationmeans.

In the image display device as described above, in the first system, acolor image is formed by at least three basic color pixels of R (red), G(green) and B (blue) as a set. Therefore, for the same display area, thenumber of color pixels that can be displayed is ⅓ of that in the secondsystem. If the number of color pixels that can be displayed is madeequal to that in the second system, the area of the spatial lightmodulator becomes three times that in the second system and the deviceis increased in size.

In the second system, if the response speed of the element fortime-divisionally switching three colors R (red), G (green) and B (blue)is not sufficiently high, light beams of the respective colors R, G andB appear independently and a displayed image cannot be recognized as acolor image. That is, a problem of so-called color breakup occurs.

As a switching frequency that sufficiently conceals color breakup, 360Hz or higher is necessary. Therefore, the response speed of theswitching element must be approximately 1 msec.

Also for the illuminating light illuminating the spatial lightmodulator, the respective basic colors must be switched at a high speed.This means that if an illuminating light source for emitting lightsimultaneously over all the range such as a lamp light source is used,only a part of emission spectrum of the light source can be effectivelyused at arbitrary timing and therefore the light utilization efficiencyis significantly deteriorated.

In the third system, though the problems of the above-described firstand second system do not occur, there are problems such as increase inthe cost of components of the spatial light modulators due to the use ofthe three spatial light modulators, complexity of adjustment foralignment of relative positions of the three spatial light modulators,increase in the cost of components of the color combination system forthe three colors, and increase in the size of the device. There is alsoa problem of poor reliability in positional deviation of the spatiallight modulators with respect to each other. Moreover, in the case wherethe device is constructed as a projection-type image display device,there is a problem of increase in F-number of a projection opticalsystem due to increase of back focusing to the projection opticalsystem. This leads to increase in the size of the projection opticalsystem and increase in the manufacturing cost.

The fourth system solves the problems of the third system and has thefollowing advantages, compared with the third system: a smaller numberof spatial light modulators can be used; the number of adjustment stepsis reduced; a color combination system for two colors is enough; thedevice is miniaturized; and reliability in positional deviation of thespatial light modulator is improved.

However, it cannot solve the problems of the second system, that is, theoccurrence of color breakup in the case the response speed of the colorswitching element is not sufficiently high and lowering of the lightutilization efficiency due to the employment of the “field sequentialsystem”, and the problems due to the need to switch the color ofilluminating light.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a new image display devicethat can solve the problems in realizing color image display by theconventional image display device.

It is another object of this invention to provide an image displaydevice that can be miniaturized and enables easy adjustment during themanufacturing process.

It is still another object of this invention to provide an image displaydevice in which the problems of the spatial light modulator and theproblems due to color switching of illuminating light do not occur.

In order to achieve the above-described objects, an image display deviceaccording to this invention includes: an illuminating light source foremitting illuminating light; a first spatial light modulator on which afirst wavelength range component of the illuminating light becomesincident and which modulates the first wavelength range component inaccordance with a pixel corresponding to the first wavelength rangecomponent; color separation and condensation means being a holographicoptical element for separating second and third wavelength rangecomponents different from the first wavelength range of the illuminatinglight and condensing the respective wavelength range components; asecond spatial light modulator on which the second and third wavelengthrange components are condensed and made incident at different pixelpositions corresponding to the second and third wavelength rangecomponents by the color separation and condensation means and whichmodulates these respective wavelength range components in accordancewith pixels corresponding to the respective wavelength range components;and color combination means for combining modulates light emitted fromthe first and second spatial light modulators.

Another image display device according to this invention includes: anilluminating light source for emitting illuminating light; a timedivision color filter on which the illuminating light becomes incidentand which sequentially and alternately transmits two differentwavelength range components of the illuminating light; color separationand condensation means for condensing one wavelength range componenttransmitted through the time division color filter as a first wavelengthrange component, and for separating the other wavelength range componenttransmitted through the time division color filter into second and thirdwavelength range components and condensing the respective wavelengthrange components; and spatial light modulators for modulating the firstwavelength range component in accordance with a pixel corresponding tothe first wavelength range component when the first wavelength rangecomponent is made incident thereon by the color separation andcondensation means, and for modulating the second and third wavelengthrange components in accordance with pixels corresponding to theserespective wavelength range components when these respective wavelengthrange components are condensed and made incident at different pixelpositions corresponding to the second and third wavelength rangecomponents.

This invention provides an image display device having the advantages ofthe above-described conventional first system combined with those of thesecond system, or having the advantages of the first system combinedwith those of the fourth system.

In the image display device according to this invention, since it is notnecessary to use three spatial light modulators, the problems of theabove-described third system are solved.

According to this invention, by combining the advantages of the firstand second systems, it is possible to display a color image with onespatial light modulator and to solve the problem of the first system,that is, low definition, and the problems of the second system, that is,color breakup and low light utilization efficiency.

In the image display device according to this invention, since one colorimage is formed physically by two basic color pixels, the definition canbe improved. As the spatial light modulator only needs to performtwo-color time-division switching display, the response speed requiredof the spatial light modulator is reduced. Therefore, the color breakupphenomenon can be relaxed and the light utilization efficiency can beimproved.

According to this invention, by combining the advantages of the firstand fourth system, it is possible to display a color image with twospatial light modulators. As the spatial light modulators, whichtime-divisionally modulates illuminating light of two colors in thefourth system, are spatially arranged on two basic color pixels as inthe first system, the problems such as color breakup and lowering oflight utilization efficiency due to employment of the “field sequentialsystem”, and the problems due to the need to switch the color of theilluminating light can be solved.

The other objects of this invention and specific advantages provided bythis invention will be further clarified by the following description ofembodiments described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a first embodiment of an image displaydevice according to this invention.

FIG. 2 is a longitudinal sectional view showing a lens arrayconstituting the image display device.

FIG. 3 is a plan view showing the structure of a blue/green spatiallight modulator of the image display device.

FIG. 4 is a plan view showing the structure of a red spatial lightmodulator of the image display device.

FIG. 5 is a plan view showing a second embodiment of the image displaydevice according to this invention.

FIG. 6 is a graph showing emission spectrum of a UHP lamp used in theimage display device.

FIG. 7 is a graph showing emission spectrum of an LED lamp used in theimage display device.

FIG. 8 is a graph showing spectral diffraction efficiency of aholographic optical element used in the image display device.

FIG. 9 is a plan view showing a third embodiment of the image displaydevice according to this invention.

FIG. 10 is a longitudinal sectional view showing the state ofmanufacturing a holographic optical element used in the image displaydevice.

FIG. 11 is a graph showing diffraction efficiency with respect towavelength and incident angle, of the holographic element used in theimage display device.

FIG. 12 is a longitudinal sectional view showing the holographic opticalelement constituting the image display device.

FIG. 13 is a plan view showing the structure of a blue/green spatiallight modulator of the image display device.

FIG. 14 is a plan view showing the structure of a red spatial lightmodulator of the image display device.

FIG. 15 is a plan view showing a fourth embodiment of the image displaydevice according to this invention.

FIG. 16 is a longitudinal sectional view showing a holographic opticalelement constituting the image display device.

FIG. 17 is a graph showing diffraction efficiency with respect towavelength and incident angle, of the holographic optical element usedin the image display device.

FIG. 18 is a plan view showing a fifth embodiment of the image displaydevice according to this invention.

FIG. 19 is a longitudinal sectional view showing a holographic opticalelement constituting the image display device.

FIG. 20 is a plan view showing a sixth embodiment of the image displaydevice according to this invention.

FIG. 21 is a longitudinal sectional view showing a holographic opticalelement constituting the image display device in the case of redillumination.

FIG. 22 is a longitudinal sectional view showing the holographic opticalelement constituting the image display device in the case of blue/greenillumination.

FIG. 23 is a side view showing a seventh embodiment of he image displaydevice according to this invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Hereinafter, embodiments of this invention will be described in detailwith reference to the drawings.

First Embodiment

As a first embodiment of an image display device according to thisinvention, an example in which this invention is applied to a two-plateprojection-type image display device will be described.

The two-plate projection-type image display device has transmissionliquid crystal elements 50, 52 as spatial light modulators, a dichroicmirror 60 as color combination means, dichroic mirrors 40, 41 as colorseparation means to the two transmission liquid crystal elements 50, 52,and the dichroic mirrors 40, 41 and a microlens array 51 as colorseparation and condensation means to the one transmission liquid crystalelement, as shown in FIG. 1.

In the two-plate projection-type image display device, illuminatinglight emitted from a UHP lamp light source 10 as an illuminating lightsource becomes incident on an illuminating optical system 20 havingfunctions such as correction of the cross-sectional shape of luminousflux, equalization of intensity, and control of divergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In this image display device, the illuminating light passed through theilluminating optical system 20 has been converted to polarized lightwith its electrical vector oscillating mainly in a directionperpendicular to the face of FIG. 1, that is, to S-polarized light to amirror 30 on which the light becomes incident after it becomes incidenton the illuminating optical system 20.

Of the illuminating light reflected and polarized by the mirror 30, onlya blue light component (second wavelength range component) is reflectedmainly by the dichroic mirror 40 for blue reflection, which constitutesthe color separation and condensation means. Then, only a green lightcomponent (third wavelength range component) is reflected mainly by thedichroic mirror 41 for green reflection, which constitutes the arrangedcolor separation and condensation means. These green light component andblue light component become incident on the blue/green transmissionliquid crystal element 50, which is a second spatial light modulatorhaving color pixels for green light modulation and color pixels for bluelight modulation. The dichroic mirror 40 for blue reflection and thedichroic mirror 41 for green reflection are arranged in such a mannerthat the incident angles on the blue/green transmission liquid crystalelement 50 of the reflected light beams of from these dichroic mirrorsare inclined by an equal angle to the vertical direction of this elementfrom the opposite sides.

On the incident side of the blue/green transmission liquid crystalelement 50, the microlens array 51 constituting the color separation andcondensation means is provided. The microlens array 51 is formed on aglass board 58. By the microlens array 51, blue light B_(L) and greenlight G_(L) to be incident on the blue/green transmission liquid crystalelement 50 are condensed and made incident on the blue/greentransmission liquid crystal element 50, corresponding to a blue colorpixel 56 and a green color pixel 57, respectively, as shown in FIG. 2.The blue color pixel 56 and the green color pixel 57 are providedcorresponding to a blue color pixel electrode 53 and a green color pixelelectrode 54 in a liquid crystal layer 55 of the blue/green transmissionliquid crystal element 50. The transmission liquid crystal element 50 isformed by a glass board 50 a, and a common transparent electrode 50 b isprovided on the surface of each pixel.

The S-polarized light incident on the blue/green transmission liquidcrystal element 50 has its intensity modulated in accordance with thepixels 56, 57 and is emitted as P-polarized light toward the dichroicmirror 60 as color combination means, which is a color combinationmirror having a dielectric multilayer film, as shown in FIG. 1.

On the other hand, a red light component (first wavelength rangecomponent) transmitted through the dichroic mirror 40 for bluereflection and the dichroic mirror 41 for green reflection is reflectedby mirrors 31, 32 and then becomes incident on the red transmissionliquid crystal element (first light modulator) 52. In this redtransmission liquid crystal element 52, the red light component of theilluminating light has its intensity modulated and is emitted asS-polarized light toward the dichroic mirror 60.

The illuminating light (modulated light) modulated and emitted by theblue/green transmission liquid crystal element 50 and the illuminatinglight (modulated light) modulated and emitted by the red transmissionliquid crystal element 52 are color-combined by the dichroic mirror 60for red reflection and emitted toward a projection optical system 70. Bythe projection optical system 70, this illuminating light is caused toform an image on a screen 80. A color image is displayed on this screen80.

In this image display device, as shown in FIG. 3, the blue/greentransmission liquid crystal element 50 has a pixel structure such thatthe basic pixel pitch in the direction of arrow X is ½ of the basicpixel pitch in the pixel structure of the red transmission liquidcrystal element 52 shown in FIG. 4 and each pixel area is approximatelyhalf the pixel area in the pixel structure of the red transmissionliquid crystal element 52.

The thickness of the liquid crystal layer of the blue/green transmissionliquid crystal element 50 and the thickness of the liquid crystal layerof the red transmission liquid crystal element 52 are optimized inaccordance with the difference of color light to be modulated.

Second Embodiment

As a second embodiment of the image display device according to thisinvention, an example in which this invention is applied to a two-plateprojection-type image display device will be described.

The two-plate projection-type image display device in the secondembodiment has transmission liquid crystal elements 50, 52 as spatiallight modulators, a polarized light beam splitter 61 as colorcombination means, dichroic mirrors 40, 41 as color separation means forthe two transmission liquid crystal elements 50, 52, and the dichroicmirrors 40, 41 and a microlens array 51 as color separation andcondensation means to the one transmission liquid crystal element 50, asshown in FIG. 5.

First, illuminating light emitted from a UHP lamp light source 10constituting an illuminating light source together with a red LED lightsource 11, which will be described later, becomes incident on anilluminating optical system 20 having functions such as correction ofthe cross-sectional shape of luminous flux, equalization of intensity,and control of divergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In this image display device, the illuminating light passed through theilluminating optical system 20 has been converted to polarized lightwith its electrical vector oscillating mainly in a directionperpendicular to the face of FIG. 5, that is, to S-polarized light to amirror 30 on which the light becomes incident after it becomes incidenton the illuminating optical system 20.

Of the illuminating light reflected and polarized by the mirror 30, onlya blue light component (second wavelength range component) is reflectedmainly by the dichroic mirror 40 for blue reflection, which constitutesthe color separation and condensation means. Then, only a green lightcomponent (third wavelength range component) is reflected mainly by thedichroic mirror 41 for green reflection, which constitutes the arrangedcolor separation and condensation means. These green light component andblue light component become incident on the blue/green transmissionliquid crystal element 50, which a second spatial light modulator havingcolor pixels for green light modulation and color pixels for blue lightmodulation. The dichroic mirror 40 for blue reflection and the dichroicmirror 41 for green reflection are arranged in such a manner that theincident angles on the blue/green transmission liquid crystal element 50of the reflected light beams of from these dichroic mirrors are inclinedby an equal angle to the vertical direction of this element from theopposite sides.

On the incident side of the blue/green transmission liquid crystalelement 50, the microlens array 51 constituting the color separation andcondensation means is provided. By the microlens array 51, blue lightand green light to be incident on the blue/green transmission liquidcrystal element 50 are condensed and made incident on the blue/greentransmission liquid crystal element 50, corresponding to a blue colorpixel 56 and a green color pixel 57, respectively, as shown in FIG. 2.The blue color pixel 56 and the green color pixel 57 are providedcorresponding to a blue color pixel electrode 53 and a green color pixelelectrode 54 in a liquid crystal layer 55 of the blue/green transmissionliquid crystal element 50.

The S-polarized light incident on the blue/green transmission liquidcrystal element 50 has its intensity modulated in accordance with thepixels 56, 57 and is emitted as P-polarized light toward the polarizedlight beam splitter 61 as color combination means, as shown in FIG. 5.

On the other hand, a red light component (first wavelength rangecomponent) transmitted through the dichroic mirror 40 for bluereflection and the dichroic mirror 41 for green reflection is passedthrough a mirror 31, a reflection holographic optical element 42 for redlight reflection, a mirror 32 and a ½ wavelength plate 90, and becomesincident on the red transmission liquid crystal element 52. In thiscase, the red light component incident on the red transmission liquidcrystal element 52 has been converted from S-polarized light toP-polarized light by the ½ wavelength plate 90. Therefore, the lightemitted from the red transmission liquid crystal element 52 toward thepolarized light beam splitter 61 is S-polarized light.

The reflection holographic optical element 42 arranged in the opticalpath between the mirror 31 and the mirror 32 has a characteristic ofmainly reflecting the spectrum of the red LED light source 11constituting the illuminating light source and transmitting incidentlight of the other wavelength ranges. The red light emitted form the redLED light source 11 is passed through a condenser lens 22, and becomesincident on the reflection holographic optical element 42. The red lightis reflected by the reflection holographic optical element 42, thenpassed through the mirror 32 and the ½ wavelength plate 90, and becomesincident on the red transmission liquid crystal element 52.

With respect to the emission spectrum of the UHP lamp light source 10,the luminance of the red wavelength range is lower than the luminance ofthe blue and green wavelength ranges, as shown in FIG. 6. In this imagedisplay device, light of a wavelength range of 630±10 nm is reflected bythe reflection holographic optical element 42 and does not reach the redtransmission liquid crystal element 52. In this image display device, asshown in FIG. 7, the emission spectrum of the red LED light source 11corresponds to the wavelength-dependent characteristic of the reflectionand diffraction efficiency of the reflection holographic optical element42 shown in FIG. 8. Therefore, light emitted from the red LED lightsource 11 is efficiently reflected by the reflection holographic opticalelement 42 for red light reflection and illuminates the red transmissionliquid crystal element 52.

As shown in FIG. 5, the P-polarized light emitted from the blue/greentransmission liquid crystal element 50 and the S-polarized light emittedfrom the red transmission liquid crystal element 52 are color-combinedby the polarized light beam splitter 61 and emitted toward a projectionoptical system 70. By the projection optical system 70, the illuminatinglight incident on the projection optical system 70 is caused to form animage on a screen 80. A color image is displayed on this screen 80.

In this image display device, as shown in FIG. 3, the blue/greentransmission liquid crystal element 50 has a pixel structure such thatthe basic pixel pitch in the direction of arrow X is ½ of the basicpixel pitch in the pixel structure of the red transmission liquidcrystal element 52 shown in FIG. 4 and each pixel area is approximatelyhalf the pixel area in the pixel structure of the red transmissionliquid crystal element 52.

The thickness of the liquid crystal layer of the blue/green transmissionliquid crystal element 50 and the thickness of the liquid crystal layerof the red transmission liquid crystal element 52 are optimized inaccordance with the difference of the color light to be modulated.

Third Embodiment

As a third embodiment of the image display device according to thisinvention, an example in which this invention is applied to a two-plateprojection-type image display device will be described.

The two-plate projection-type image display device in the thirdembodiment has reflection liquid crystal spatial light modulators 101,102 as spatial light modulators, a polarized light beam splitter 140 andspecific wavelength range linear polarization rotation means (multilayerphase difference filter) 120 as color combination means, dichroicmirrors 40, 41 as color separation means for the two reflection liquidcrystal spatial light modulators 101, 102, and a transmissionpolarization-selective holographic optical element 100 as colorseparation and condensation means to the one reflection liquid crystalspatial light modulator, as shown in FIG. 9.

In this two-plate projection-type image display device, first,illuminating light emitted from a UHP lamp light source 10 as anilluminating light source becomes incident on an illuminating opticalsystem 20 having functions such as correction of the cross-sectionalshape of luminous flux, equalization of intensity, and control ofdivergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In the image display device shown in FIG. 9, the illuminating lightpassed through the illuminating optical system 20 has been converted topolarized light with its electrical vector oscillating mainly in adirection perpendicular to the face of FIG. 9, that is, to S-polarizedlight to the dichroic mirror 40 for blue reflection, the dichroic mirror41 for green reflection and a mirror 30 on which the light becomesincident after it becomes incident on the illuminating optical system20.

The illuminating light is reflected by the dichroic mirror 40 for bluereflection and the dichroic mirror 41 for green reflection and becomesincident on the holographic PDLC (transmission polarization-selectiveholographic optical element) 100 at difference incident angles.

The holographic PDLC 100 used in this image display device ismanufactured by inserting PDLC, which is a mixture of polymer beforephotopolymerization (hereinafter referred to as prepolymer), nematicliquid crystal, initiator and pigment, between a pair of glass boards103, 104, as shown in FIG. 10.

In manufacturing this holographic PDLC 100, rate by weight of nematicliquid crystal is approximately 40% of the total weight. For thethickness of this holographic PDLC 100 (hereinafter referred to as cellgap), an optimum value within a range of 3 to 15 μm is selected inaccordance with the specifications of the holographic PDLC 100.

Next, to record interference fringes on the holographic PDLC 100, objectlight 105 and reference light 106 are cast onto the holographic PDLC 100from a laser light source, not shown, and variation in light intensity(A) is generated by the interference of these lights.

In this case, at a part where the interference fringes are bright, thatis, where the photon energy is large, the prepolymer in the holographicPDLC is photopolymerized into polymer by this energy. This polymerizedpart is sequentially supplied with the prepolymer from the surroundingparts. As a result, an area where the polymerized prepolymer is denseand an area where it is sparse are formed. In the area where theprepolymer is dense, the concentration of nematic liquid crystal ishigh. In this manner, two areas are formed, that is, a polymerhigh-density area 107 and a liquid crystal high-density area 108.

This holographic PDLC 100 is of transmission type because it ismanufactured by casting the object light 105 and the reference light 106to the holographic PDLC 100 from the same side.

The polymer high-density area 107 in the holographic PDLC 100manufactured as described above is isotropic with respect to therefractive index. The refractive index is, for example, 1.5. On theother hand, in the liquid crystal high-density area 108 of theholographic PDCL 100, nematic liquid crystal molecules are arrayed withtheir longitudinal direction directed substantially perpendicularly tothe boundary with the polymer high-density area 107. Therefore, thisliquid crystal high-density area 108 is dependent on the direction ofincident polarized light. Of reproduced light 110 inclined with respectto a ray incident surface 109 of the holographic PDLC 100 and incidentin a direction substantially perpendicular to the direction of theboundary between the polymer high-density area 107 and the liquidcrystal high-density area 108, an S-polarized component becomes anordinary ray in the liquid crystal high-density area 108, as shown inFIG. 10.

If the refractive index nlo of the ordinary ray in the liquid crystalhigh-density area 108 is set at a value substantially equal to therefractive index np of the polymer high-density area 107, for example,if the difference in the refractive index is less than 0.01, modulationof the incident S-polarized component based on the refractive index isvery small and almost no diffraction occurs. Generally, the differenceΔn between the refractive index nlo of the ordinary ray of the nematicliquid crystal and the refractive index nle of an extraordinary ray isapproximately 0.1 to 0.2. Therefore, even with the reproduced light 111in the same incident direction, a P-polarized component, which is anextraordinary ray, is different in refractive index between the polymerhigh-density area 107 and the liquid crystal high-density area 108 and adiffraction effect occurs. For example, the diffraction efficiency foran extraordinary ray can be 50% or more, and the diffraction efficiencyfor an ordinary ray can be 10% or less.

In this manner, the holographic PDLC 100 functions as a phase modulationhologram with respect to the P-polarized component, which is anextraordinary ray. That is, in this holographic PDLC 100, as shown inFIG. 10, the S-polarized component, which is an ordinary ray, of thereproduced light 111, is transmitted as it is without being diffracted,whereas the P-polarized component, which an extraordinary ray, of thereproduced light 111, is diffracted and emitted substantiallyperpendicularly from the holographic PDLC 100.

The diffraction efficiency for P-polarized light of this holographicPDLC 100 depends on the incident angle and wavelength, as shown in FIG.11. According to this characteristic, a diffraction efficiency of 50% orhigher with respect to green light having a center wavelength of 550 nmis realized when the incident angle is 46°±8°, and a diffractionefficiency of 50% or higher with respect to blue light having a centerwavelength of 440 nm is realized when the incident angle is 41°±7.5°. Inthis manner, the incident angle on the holographic PDLC 100 thatrealizes the optimum diffraction efficiency is different between bluelight and green light. Therefore, the angle of illuminating lightincident on the holographic PDLC 100 is changed between blue light andgreen light.

In the above-described holographic PDLC 100, the hologram layer has athickness of 4 μm, a degree of modulation of refractive index of 0.06,an exposure wavelength of 532 nm, an incident angle of object light of0° and an incident angle of reference light of 45°.

Actually, the holographic PDLC 100 has a single structure made up of ablue/green light hologram layer 100 a formed on a glass board 100 b andis integrally constituted with the blue/green light reflection liquidcrystal spatial light modulator 101, as shown in FIG. 12. Theholographic PDLC 100 formed on a glass board 101 a has a function ofcylindrical lens having condensing capability only in one direction sothat illuminating light is condensed on a blue light pixel electrode 115and a green light pixel electrode 116 of the blue/green light reflectionliquid crystal spatial light modulator 101. A liquid crystal layer 123is formed on the blue light pixel electrode 115 and the green lightpixel electrode 116. The blue light pixel electrode 115 and the greenlight pixel electrode 116 are formed on a glass board 124.

The center of the holographic lens for each color is arranged to besubstantially coincident with the center of the corresponding colorpixel electrode. Color separation of blue light and green light of theilluminating light is realized by utilizing the difference in theincident angle between blue light (B_(L)) and green light (G_(L)) byapproximately 5° and the wavelength distribution of the holographic PDLC100.

In the case of “white” display, the illuminating light, color-separatedand condensed on the respective color pixel electrodes 115, 116, has itsdirection of incident polarization rotated 90° and is reflected asS-polarized light. Therefore, in this case, the reflected light isemitted substantially perpendicularly to the blue/green light reflectionliquid crystal spatial light modulator 101, without being diffracted bythe blue light hologram layer and the green light hologram layer.

This reflected light becomes incident on the specific wavelength rangelinear polarization rotation means (multilayer phase difference filter)120 such as “Color Select” manufactured by Color Link, as shown in FIG.9. This specific wavelength range linear polarization rotation means 120is an optical element formed by stacking phase difference plates androtates the linear polarization direction of a specific wavelength rangeonly (in this case, blue and green light) by 90°. That is, this specificwavelength range linear polarization rotation means 120 converts theS-polarized light modulated by the blue/green light reflection liquidcrystal spatial light modulator 101 to P-polarized light.

The blue and green light thus converted to P-polarized light istransmitted through the polarized light beam splitter 140, thentransmitted through red light linear polarization rotation means 121 anda polarizing plate 150 for transmitting P-polarized light, and becomesincident on the projection optical system 70. The polarized light beamsplitter 140 is constructed to transmit P-polarized light and reflectS-polarized light. The blue and green light incident on the projectionoptical system 70 forms an image on a screen, not shown.

Meanwhile, the red light transmitted through the dichroic mirror 40 forblue reflection and the dichroic mirror 41 for green reflection isreflected by the mirror 30, then detected by a polarizing plate 130 fortransmitting P-polarized light, and becomes incident on the specificwavelength range linear polarization rotation means 120. This specificwavelength range linear polarization rotation means 120 does not have apolarized light rotation function for red light. Therefore, the redlight is transmitted as it is through the specific wavelength rangelinear polarization rotation means 120. The red light is thentransmitted through the polarized light beam splitter 140 and becomesincident on the red light reflection liquid crystal spatial lightmodulator 102.

Of the modulated light reflected by this red light reflection liquidcrystal spatial light modulator 102, S-polarized light corresponding to“white” display is reflected by the polarized light beam splitter 140and becomes incident on the red light linear polarization rotation means121. This modulated light has its direction of polarization rotated 90°by the red light linear polarization rotation means 121 and becomesP-polarized light. This modulated light is detected by the polarizingplate 150 and becomes incident on the projection optical system 70. Thered light incident on the projection optical system 70 forms an image onthe screen, not shown. In this manner, a color image is displayed on thescreen.

In this image display device, as shown in FIG. 13, the pixel structureof the blue/green reflection liquid crystal spatial light modulator 101is perfectly equal to the pixel structure of the red reflection liquidcrystal spatial light modulator 102 shown in FIG. 14. In the redreflection liquid crystal spatial light modulator 102, two basic pixelsas a pair corresponding to one blue light pixel 125 and one green lightpixel 126 are equally driven as one pixel.

The thickness of the liquid crystal layer of the blue/green reflectionliquid crystal spatial light modulator 101 and the thickness of theliquid crystal layer of the red reflection liquid crystal spatial lightmodulator 102 are optimized in accordance with the difference of thecolor light to be modulated.

Fourth Embodiment

As a fourth embodiment of the image display device according to thisinvention, an example in which this invention is applied to a two-plateprojection-type image display device will be described.

The two-plate projection-type image display device in the fourthembodiment has reflection liquid crystal spatial light modulators 101,102 as spatial light modulators, a polarized light beam splitter 140 ascolor combination means, dichroic mirrors 40, 41 as color separationmeans to the two reflection liquid crystal spatial light modulators 101,102, and a holographic PDLC (transmission polarization-selectiveholographic optical element) 111 as color separation and condensationmeans to the one reflection liquid crystal spatial light modulator, asshown in FIG. 15.

In this two-plate projection-type image display device, illuminatinglight emitted from a UHP lamp light source 10 as an illuminating lightsource becomes incident on an illuminating optical system 20 havingfunctions such as correction of the cross-sectional shape of luminousflux, equalization of intensity, and control of divergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In the image display device shown in FIG. 15, the illuminating lightpassed through the illuminating optical system 20 has been converted topolarized light with its electrical vector oscillating mainly in adirection parallel to the face of FIG. 15, that is, to P-polarized lightto the dichroic mirror 40 for blue reflection and the dichroic mirror 41for green reflection on which the light becomes incident after itbecomes incident on the illuminating optical system 20.

The illuminating light is reflected by the dichroic mirror 40 for bluereflection and the dichroic mirror 41 for green reflection and becomesincident on the holographic PDLC 111 at difference incident angles.

The holographic PDLC 111 used in this image display device ismanufactured by inserting PDLC, which is a mixture of polymer beforephotopolymerization, nematic liquid crystal, initiator and pigment,between a pair of glass boards. The manufacturing method for and thefunction of the holographic PDLC 111 used in this embodiment arebasically similar to those of the holographic PDLC 111 of the thirdembodiment. However, in this embodiment, the holographic PDLC 11 isconstructed to diffract S-polarized light.

Specifically, the holographic PDLC 111 functions as a phase modulationhologram with respect to an S-polarized component, which is anextraordinary ray. That is, in this holographic PDLC 111, as shown inFIG. 16, a P-polarized component, which is an ordinary ray, ofreproduced light 110, is transmitted as it is without being diffracted,whereas an S-polarized component, which an extraordinary ray, of thereproduced light 110, is diffracted and emitted substantiallyperpendicularly from the holographic PDLC 111.

The diffraction efficiency for P-polarized light of this holographicPDLC 111 depends on the incident angle and wavelength, as shown in FIG.17. According to this characteristic, a diffraction efficiency of 50% orhigher with respect to green light having a center wavelength of 550 nmis realized when the incident angle is 46°±8°, and a diffractionefficiency of 50% or higher with respect to blue light having a centerwavelength of 440 nm is realized when the incident angle is 41°±7.5°. Inthis manner, the incident angle on the holographic PDLC 111 thatrealizes the optimum diffraction efficiency is different between bluelight and green light. Therefore, the angle of illuminating lightincident on the holographic PDLC 111 is changed between blue light andgreen light.

In the holographic PDLC 111 used in this embodiment, the hologram layerhas a thickness of 4 μm, a degree of modulation of refractive index of0.06, an exposure wavelength of 532 nm, an incident angle of objectlight of 0° and an incident angle of reference light of 45°.

Actually, the holographic PDLC 111 used here has a single structure madeup of a blue/green light hologram layer and is integrally constitutedwith the blue/green light reflection liquid crystal spatial lightmodulator 101, as shown in FIG. 12. The holographic PDLC 111 has afunction of cylindrical lens having condensing capability only in onedirection so that illuminating light is condensed on a blue light pixelelectrode 115 and a green light pixel electrode 116 of the blue/greenlight reflection liquid crystal spatial light modulator 101.

The center of the holographic lens for each color is arranged to besubstantially coincident with the center of the corresponding colorpixel electrode. Color separation of blue light and green light of theilluminating light is realized by utilizing the difference in theincident angle between blue light (B_(L)) and green light (G_(L)) byapproximately 5° and the wavelength distribution of the holographic PDLC111.

In the case of “white” display, the illuminating light, color-separatedand condensed on the respective color pixel electrodes 115, 116, has itsdirection of incident polarization rotated 90° and is reflected asS-polarized light. Therefore, in this case, the reflected light isemitted substantially perpendicularly to the blue/green light reflectionliquid crystal spatial light modulator 101, without being diffracted bythe blue light hologram layer and the green light hologram layer.

This reflected light is transmitted through the polarized light beamsplitter 140 for transmitting P-polarized light and reflectingS-polarized light, then transmitted through red light linearpolarization rotation means 121 and a polarizing plate 150 fortransmitting P-polarized light, and becomes incident on a projectionoptical system 70. The polarized light beam splitter 140 is constructedto transmit P-polarized light and reflect S-polarized light. The blueand green light incident on the projection optical system 70 forms animage on a screen, not shown.

Meanwhile, red light emitted from a red LED light source 11 providedseparately from the UHP lamp light source 10 is passed through acondenser lens 22, the transmitted through the polarized light beamsplitter 140, and becomes incident on the red light reflection liquidcrystal spatial light modulator 102. Of the modulated light reflected bythis red light reflection liquid crystal spatial light modulator 102,S-polarized light corresponding to “white” display is reflected by thepolarized light beam splitter 140, then has its direction ofpolarization rotated 90° by the red light linear polarization rotationmeans 121, and becomes P-polarized light. This modulated light isdetected by the polarizing plate 150 and becomes incident on theprojection optical system 70. The red light incident on the projectionoptical system 70 forms an image on the screen, not shown. In thismanner, a color image is displayed on the screen.

In this image display device, as shown in FIG. 13, the pixel structureof the blue/green reflection liquid crystal spatial light modulator 101is perfectly equal to the pixel structure of the red reflection liquidcrystal spatial light modulator 102 shown in FIG. 14. In the redreflection liquid crystal spatial light modulator 102, two basic pixelsas a pair corresponding to one blue light pixel 125 and one green lightpixel 126 are equally driven as one pixel.

The thickness of the liquid crystal layer of the blue/green reflectionliquid crystal spatial light modulator 101 and the thickness of theliquid crystal layer of the red reflection liquid crystal spatial lightmodulator 102 are optimized in accordance with the difference of thecolor light to be modulated.

Fifth Embodiment

As a fifth embodiment of the image display device according to thisinvention, an example in which this invention is applied to a two-plateprojection-type image display device will be described.

The two-plate projection-type image display device in the fifthembodiment has reflection liquid crystal spatial light modulators 101,102 as spatial light modulators, a polarized light beam splitter 141 ascolor combination means, a holographic PDLC 122 as color separationmeans to the two reflection liquid crystal spatial light modulators 101,102, and a holographic PDLC 112 as color separation and condensationmeans to the one reflection liquid crystal spatial light modulator 101,as shown in FIG. 18.

First, illuminating light emitted from a UHP lamp light source 10 as anilluminating light source becomes incident on an illuminating opticalsystem 20 having functions such as correction of the cross-sectionalshape of luminous flux, equalization of intensity, and control ofdivergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In this embodiment, the illuminating light passed through theilluminating optical system 20 has been converted to polarized lightwith its electrical vector oscillating mainly in a direction parallel tothe face of FIG. 18, that is, to P-polarized light to a mirror 30 onwhich the light becomes incident after it becomes incident on theilluminating optical system 20.

The illuminating light is detected by a polarizing plate 151 fortransmitting P-polarized light, then only has its red light componentconverted to S-polarized light by red light linear polarization rotationmeans (multilayer phase difference filter) 121, and becomes incident onthe holographic PDLC (transmission polarization-selective holographicoptical element) 122. This holographic PDLC 122 diffracts onlyP-polarized light and transmits S-polarized light, like the holographicPDLC 100 of the above-described third embodiment. Therefore, blue andgreen light is diffracted by this holographic PDLC 122 and red light istransmitted through the holographic PDLC 122 as it is.

The blue and green light diffracted by the holographic PDLC 122 passesthrough a place of incidence of a coupling prism 160 and becomesincident on the holographic PDLC 112 optically joined with the couplingprism 160. Also this holographic PDCL 112 has a function of diffractingonly P-polarized light and transmitting S-polarized light, like theholographic PDCL 100 of the above-described third embodiment.

The holographic PDLC 112 of this embodiment has a stacked two-layerstructure in which a blue light hologram layer 113 and a green lighthologram layer 114 are provided as two layers with glass boards 100 c,100 d, and the holographic PDLC 112 is integrally constructed with theblue/green light reflection liquid crystal spatial light modulator 101,as shown in FIG. 19. The holographic PDLC 112 has a function ofcylindrical lens having condensing capability only in one direction sothat illuminating light is condensed on a blue light pixel electrode 115and a green light pixel electrode 116 of the blue/green light reflectionliquid crystal spatial light modulator 101. The center of theholographic lens for each color is arranged to be substantiallycoincident with the center of the corresponding color pixel electrode.

The blue light pixel electrode 115 and the green light pixel electrode116 are formed on a glass board 127. A liquid crystal layer 128 isformed on the electrodes 115, 116. Moreover, a glass board 129 isprovided thereon.

In the case of “white” display, the illuminating light, color-separatedand condensed on the respective color pixel electrodes 115, 116, has itsdirection of incident polarization rotated 90° and is reflected asS-polarized light. Therefore, in this case, the reflected light isemitted substantially perpendicularly to the blue/green light reflectionliquid crystal spatial light modulator 101, without being diffracted bythe blue light hologram layer 113 and the green light hologram layer114.

The modulated light, which is S-polarized light reflected by theblue/green light reflection liquid crystal spatial light modulator 101,passes through the coupling prism 160 again and has its direction ofpolarization rotated by 90° by a ½ wavelength plate 170 to becomeP-polarized light, as shown in FIG. 18. Then, this modulated light istransmitted through the polarized light beam splitter 141 fortransmitting P-polarized light and reflecting S-polarized light andbecomes incident on a projection optical system 70. The blue and greenlight incident on the projection optical system 70 forms an image on ascreen, not shown.

Meanwhile, the red light, which is S-polarized light transmitted throughthe holographic PDLC 122, is reflected by the mirror 30, then convertedto P-polarized light by the ½ wavelength plate 170, and becomes incidenton the polarized light beam splitter 141. Then, the red light istransmitted through a polarized light separation film of this polarizedlight beam splitter 141 and becomes incident on the red light reflectionliquid crystal spatial light modulator 102. Of the modulated lightreflected by the red light reflection liquid crystal spatial lightmodulator 102, S-polarized light corresponding to “white” display isreflected by the polarized light separation film of the polarized lightbeam splitter 141 and combined with the blue and green light. Thismodulated light becomes incident on the projection optical system 70.The red light incident on the projection optical system 70 forms animage on the screen, not shown. In this manner, a color image isdisplayed on the screen.

In this image display device, as shown in FIG. 13, the pixel structureof the blue/green reflection liquid crystal spatial light modulator 101is perfectly equal to the pixel structure of the red reflection liquidcrystal spatial light modulator 102 shown in FIG. 14. In the redreflection liquid crystal spatial light modulator 102, two basic pixelsas a pair corresponding to one blue light pixel 125 and one green lightpixel 126 are equally driven as one pixel.

The thickness of the liquid crystal layer of the blue/green reflectionliquid crystal spatial light modulator 101 and the thickness of theliquid crystal layer of the red reflection liquid crystal spatial lightmodulator 102 are optimized in accordance with the difference of thecolor light to be modulated.

Sixth Embodiment

As a sixth embodiment of the image display device according to thisinvention, an example in which this invention is applied to asingle-plate projection-type image display device will be described.

The single-plate projection-type image display device in the sixthembodiment has a holographic PDLC (transmission polarization-selectiveholographic optical element) 117 as color separation and condensationmeans to a reflection liquid crystal spatial light modulator 118, asshown in FIG. 20.

In this image display device, illuminating light emitted from a UHP lamplight source 10 as an illuminating light source becomes incident on anilluminating optical system 20 having functions such as correction ofthe cross-sectional shape of luminous flux, equalization of intensity,and control of divergence angle.

The illuminating optical system 20 has polarization conversion means 21called P-S polarization converter having a function of uniformlyconverting unpolarized luminous fluxes to either P-polarized light orS-polarized light at an efficiency of 50% or higher. This illuminatingoptical system 20 includes plural condenser lenses and the polarizationconversion means 21.

In this image display device, the illuminating light passed through theilluminating optical system 20 has been converted to polarized lightwith its electrical vector oscillating mainly in a direction parallel tothe face of FIG. 20, that is, to P-polarized light to dichroic mirrors43, 41 and 40 on which the light becomes incident after it becomesincident on the illuminating optical system 20.

As this illuminating light sequentially passes through the dichroicmirror 43 for red reflection, the dichroic mirror 41 for greenreflection and the dichroic mirror 40 for blue reflection, its redcomponent, green component and blue component are reflected. These redcomponent, green component and blue component of the illuminating lightbecome incident on a color wheel 180. This color wheel 180time-divisionally switches red light and cyan (blue+green) light. Thecolor light components passed through the color wheel 180 becomeincident on the holographic PDLC 117 at different incident angles,respectively.

The structure of the holographic PDLC 117 used in this embodiment isadapted for diffracting P-polarized light and not diffractingS-polarized light, like the holographic PDLC 100 used in theabove-described third embodiment. This holographic PDLC 117 has astructure in which hologram layers for R, G, B light 131, 132, 133 arestacked as three layers with glass board 134, 135, 136, and theholographic PDLC 117 is integrally constructed with the reflectionliquid crystal spatial light modulator 118, as shown in FIGS. 21 and 22.

The holographic PDLC 117 has a function of cylindrical lens havingcondensing capability only in one direction so that illuminating lightis condensed on a corresponding basic pixel of each color of thereflection liquid crystal spatial light modulator 118.

In the case where the red light component of the illuminating light isselected by the color wheel 180 and made incident on the holographicPDLC 117, the illuminating light is diffracted only by the red lighthologram layer 131 of the holographic PDCL 117 and condensed on allbasic pixel electrodes 119 a, 119 b of the reflection liquid crystalspatial light modulator 118, as shown in FIG. 21. In image display,since two adjacent basic pixel electrodes 119 a, 119 b are used as onepixel electrode 119, these adjacent two pixel electrodes 119 a, 119 bare equally driven as one pixel electrode 119.

Also in the reflection liquid crystal spatial light modulator 118, thepixel electrodes 119 are formed on a glass board 137. A liquid crystallayer 138 is provided on the pixel electrodes 119. The holographic PDLC117 is provided over this with a glass board 139 provided between theholographic PDLC 117 and the liquid crystal layer 138.

Next, in the case where the blue light component and the green lightcomponent of the illuminating light are selected by the color wheel 180and made incident on the holographic PDLC 117, these color components ofthe illuminating light are diffracted by the blue light hologram layer133 and the green light hologram layer 132, respectively, and condensedon the corresponding basic pixel electrodes 119 a, 119 b of theholographic PDLC 117, as shown in FIG. 22.

In this reflection liquid crystal spatial light modulator 118, the twobasic pixel electrodes for red light modulation as a pair in red lightmodulation, and the basic pixel electrode for blue light modulation andthe basic pixel electrode for green light modulation in blue and greenlight modulation, that is, four pixel electrodes in total, are driven asone pixel to realize color image display. Of these four pixel electrodesin total, the two basic pixel electrodes for red light modulation willbe later used as the basic pixel electrode for blue light modulation andthe basic pixel electrode for green light modulation. Therefore, it canbe considered that there are physically two pixel electrodes.

In the holographic PDLC 117, since the hologram layers 131 to 133 arestacked, the diffracted light diffracted by the red hologram layer 131and the green hologram layer 132, which are upper layers, is diffractedagain by the blue hologram layer 133, which is a lower layer. Therefore,a part of the illuminating light does not illuminate the reflectionliquid crystal spatial light modulator 118.

To prevent this, it is necessary to sufficiently narrow the spreadingangle of the illuminating light to be cast, for example, toapproximately ±3°, and narrow the wavelength range of each color light,for example, to approximately ±20 nm. Moreover, it is necessary toreduce the allowable diffraction angle of each hologram layer.Therefore, in this embodiment, the illuminating light is set to beincident on the hologram layers at a sufficiently large angle, forexample, 65°, using a coupling prism 160.

In the case of “white” display, the illuminating light, color-separatedand condensed on the respective color pixel electrodes 119 a, 119 b ofthe reflection liquid crystal spatial light modulator 118, has itsdirection of incident polarization rotated 90° and is reflected asS-polarized light. Therefore, in this case, the reflected light isemitted substantially perpendicularly to the reflection liquid crystalspatial light modulator 118, without being diffracted by the respectivecolor light hologram layers (R, G, B).

This reflected light passes through the coupling prism 160 again, thendetected by a polarizing plate 150 for transmitting S-polarized light,and becomes incident on a projection optical system 70, as shown in FIG.20. The reflected light incident on the projection optical system 70forms an image on a screen, not shown. In this manner, a color image isdisplayed on the screen.

Seventh Embodiment

As a seventh embodiment of the image display device according to thisinvention, an example in which this invention is applied to a virtualimage display device will be described.

The virtual image display device has EL image display elements 101, 102as two spatial light modulators, a dichroic mirror 60, and an eyepiecelens 190, as shown in FIG. 23.

In this image display device, display light from the EL image displayelement 101 for red light emission and display light from the EL imagedisplay element 102 for green/blue light emission are combined by thedichroic mirror 60 for red reflection, then passes through the eyepiecelens 190, and makes virtual image display to an eye 191.

In this image display device, as shown in FIG. 3, the EL display element102 for blue/green light emission has a pixel structure such that thebasic pixel pitch in the direction of arrow X is ½ of the basic pixelpitch in the pixel structure of the EL display element 101 for red lightemission shown in FIG. 4 and each pixel area is approximately half thepixel area in the pixel structure of the EL display element 101 for redlight emission.

INDUSTRIAL APPLICABILITY

As described above, the image display device according to this inventionrealizes color image display by using one or two spatial lightmodulators. Therefore, the number of spatial light modulators to be usedcan be reduced and the device itself can be miniaturized. Moreover, thepositions of the spatial light modulators can be easily adjusted andaccurate positional alignment of the spatial light modulators can beeasily realized.

Moreover, the image display device according to this invention can avoidincrease in F-number of a projection optical system due to increase ofback focusing to the projection optical system required in the case of aprojection-type image display device, and therefore enables reduction inthe manufacturing cost.

In the image display device according to this invention, even when aspatial light modulator with a relatively low response speed is used,since the spatial light modulator has a two-plate structure, thedefinition of a displayed image is not significantly lowered and colorimage display having no color breakup with high light utilizationefficiency can be realized.

In the image display device according to this invention, if a spatiallight modulator that has a relatively high response speed and canrealize two-color switching display at a level where color breakup doesnot occur is used, color image display with high light utilizationefficiency can be realized by a single-plate structure.

In the image display device according to this invention, by separatingand condensing color light corresponding to two basic color pixelsphysically formed in one spatial light modulator onto the two basiccolor pixels, it is possible to realize a highly efficient image displayelement.

Moreover, by using a polarization-selective holographic optical elementusing an anisotropic material such as a liquid crystal material as aholographic optical element, it is possible to realize more efficientcolor image display.

In the image display device according to this invention, when twospatial light modulators are used, by using the spatial light modulatorhaving a color pixel for modulating one wavelength range as a spatiallight modulator for red light modulation and using the spatial lightmodulator having a color pixel for modulating two different wavelengthranges as a spatial light modulator for blue and green light modulation,it is possible to realize highly efficient color image display with goodcolor balance.

When one spatial light modulator is used, by using light beams of twocolors emitted from a time division color filter as red light and cyanlight and illuminating the spatial light modulator with these lights, itis possible to realize highly efficient color image display with goodcolor balance.

In the image display device according to this invention, when twospatial light modulators are used, by using a second light source thatmainly emits red light and illuminating the spatial light modulatorhaving a color pixel for modulating one wavelength range with the secondlight source, it is possible to realize highly efficient color imagedisplay with good color balance.

1. An image display device comprising: an illuminating light source foremitting illuminating light; a first spatial light modulator on which afirst wavelength range component of the illuminating light becomesincident and which modulates the first wavelength range component inaccordance with a pixel corresponding to the first wavelength rangecomponent; color separation and condensation means being a holographicoptical element for separating second and third wavelength rangecomponents different from the first wavelength range component of theilluminating light and condensing the respective wavelength rangecomponents; a second spatial light modulator on which the second andthird wavelength range components are condensed and made incident atdifferent pixel positions corresponding to the second and thirdwavelength range components by the color separation and condensationmeans and which modulates these respective wavelength range componentsin accordance with pixels corresponding to the respective wavelengthrange components; and color combination means for combining modulatedlight emitted from the first and second spatial light modulators.
 2. Theimage display device as claimed in claim 1, wherein the holographicoptical element is a polarization-selective holographic optical elementcontaining a liquid crystal material.
 3. The image display device asclaimed in claim 1, wherein illuminating light incident on theholographic optical element is P-polarized light.
 4. The image displaydevice as claimed in claim 1, wherein the holographic optical elementhas a diffraction efficiency of 50% or more for P-polarized light and adiffraction efficiency of 10% or less for S-polarized light.
 5. Theimage display device as claimed in claim 1, wherein in the holographicoptical element, two types of holographic lenses, that is, a holographiclens for green diffraction and a holographic lens for blue diffraction,are formed by stacking plural hologram layers or by multiple exposure ofone hologram layer.
 6. The image display device as claimed in claim 1,further comprising color separation means made up of a holographicoptical element on which the illuminating light from the illuminatinglight source becomes incident, wherein the color separation meansdiffracts one of blue and green light, which is the second and thirdwavelength range components of the illuminating light, and red light,which is the first wavelength range component of the illuminating light,and does not diffract the other, thereby separating the blue and greenlight from the red light, and the color separation means causes the redlight to be incident on the first spatial light modulator and causes theblue and green light to be incident on the holographic optical elementwhich is the color separation and condensation means.
 7. The imagedisplay device as claimed in claim 1, wherein the second spatial lightmodulator has, in different pixels corresponding to the second and thirdwavelength range components, a color filter corresponding to eachwavelength range.
 8. The image display device as claimed in claim 7,wherein the first and second spatial light modulators are reflectionspatial light modulators, optical element is a polarization-selectiveholographic optical element containing a liquid crystal material.
 9. Theimage display device as claimed in claim 7, wherein the colorcombination means is a color combination mirror having a dielectricmultilayer film.
 10. The image display device as claimed in claim 7,wherein the color combination means is a polarized light beam splitter.11. The image display device as claimed in claim 7, wherein the colorcombination means is a holographic optical element.
 12. The imagedisplay device as claimed in claim 7, wherein the pixel in the firstspatial light modulator is a pixel for a red light modulation, and thepixels of the second spatial light modulator are a pixel for blue lightmodulation and a pixel for green light modulation.
 13. The image displaydevice as claimed in claim 7, wherein the illuminating light sourceincludes plural light sources having difference emission wavelengthranges and illuminating light emitted from at least one light sourceilluminates only one of the first and second spatial light modulators.14. The image display device as claimed in claim 7, further comprisingcolor separation means for separating the illuminating light into thefirst wavelength range component and a range component including thesecond and third wavelength range components, causing the firstwavelength range component to be incident on the first spatial lightmodulator, and causing the range component including the second andthird wavelength range components to be incident on the color separationand condensation means.
 15. The image display device as claimed in claim7, wherein the first and second spatial light modulators have equalpixel structures and display areas.
 16. The image display device asclaimed in claim 7, wherein the number of pixels in the first spatiallight modulator is ½ of the number of pixels in the second spatial lightmodulator and its display area is equal to that of the second spatiallight modulator.
 17. An image display device comprising: an illuminatinglight source for emitting illuminating light; a time division colorfilter on which the illuminating light becomes incident and whichsequentially and alternately transmits two different wavelength rangecomponents of the illuminating light; color separation and condensationmeans for condensing one wavelength range component transmitted throughthe time division color filter as a first wavelength range component,and for separating the other wavelength range component transmittedthrough the time division color filter into second and third wavelengthrange components and condensing the respective wavelength rangecomponents; and spatial light modulators for modulating the firstwavelength range component in accordance with a pixel corresponding tothe first wavelength range component when the first wavelength rangecomponent is made incident thereon by the color separation andcondensation means, and for modulating the second and third wavelengthrange components in accordance with pixels corresponding to theserespective wavelength range components when these respective wavelengthrange components are condensed and made incident at different pixelpositions corresponding to the second and third wavelength rangecomponents.
 18. The image display device as claimed in claim 17, whereintwo wavelength range components transmitted by the time division colorfilter are red light and cyan light.
 19. The image display device asclaimed in claim 17, wherein the spatial light modulator is a reflectionspatial light modulator.
 20. The image display device as claimed inclaim 17, wherein the illuminating light source includes pluralilluminating light sources having difference emission wavelength rangesand illuminating light emitted from at least one illuminating lightsource illuminates only one of the spatial light modulators.
 21. Theimage display device as claimed in claim 17, further comprising colorseparation means for separating the different wavelength rangecomponents of the illuminating light to the first spatial lightmodulator and the second spatial light modulator.
 22. The image displaydevice as claimed in claim 17, wherein the color separation andcondensation means is a holographic optical element.
 23. The imagedisplay device as claimed in claim 22, wherein the holographic opticalelement is a polarization-selective holographic optical elementcontaining a liquid crystal material.
 24. The image display device asclaimed in claim 22, wherein illuminating light incident on theholographic optical element is P-polarized light.
 25. The image displaydevice as claimed in claim 22, wherein the holographic optical elementhas a diffraction efficiency of 50% or more for P-polarized light and adiffraction efficiency of 10% or less for S-polarized light.
 26. Theimage display device as claimed in claim 22, wherein in the holographicoptical element, three types of holographic lenses, that is, aholographic lens for red diffraction, a holographic lens for greendiffraction and a holographic lens for blue diffraction, are formed bystacking plural hologram layers or by multiple exposure of one hologramlayer.
 27. The image display device as claimed in claim 26, wherein thearea of one said holographic lens for red diffraction is ½ of the areaof one said holographic lens for green diffraction and said holographiclens for blue diffraction.